This Flex app is an interesting one.
It shows the percentages of deployment of the main RIA plugins (Flash Player for Flex, Silverlight Player for Silverlight, JRE for JavaFX), in real time, based on about 41 sites, during the last 30 days.
Apparently, regardless of the OS and the browser, almost 70% of the desktops do not have the Silverlight plugin yet. I am not surprised, I installed it today only.
On the other side, almost every desktop runs Flash Player (97%).
And 26% of the desktops do not have a JRE.